nvdnkpr / node-levelgraph

A graph database built on top of LevelUp

LevelGraph

LevelGraph is a Graph Database. Unlike many other graph database, LevelGraph is built on the uber-fast key-value store LevelDB through the powerful LevelUp library. You can use it inside your node.js application.

LevelGraph loosely follows the Hexastore approach as presente in the article: Hexastore: sextuple indexing for semantic web data management C Weiss, P Karras, A Bernstein - Proceedings of the VLDB Endowment, 2008. Following this approach, LevelGraph uses six indices for every triple, in order to access them as fast as it is possible.

Install

npm install levelup levelgraph --save

At the moment it requires node v0.10.x, but the port to node v0.8.x should be straighforward. If you need it, just open a pull request.

Usage

Initializing a database is very easy:

var levelup = require("levelup");
var levelgraph = require("../");
var db = levelgraph(levelup(dir));

Get and Put

Inserting a triple in the database is extremey easy:

var triple = { subject: "a", predicate: "b", object: "c" };
db.put(triple, function(err) {
  // do something after the triple is inserted
});

Retrieving it through pattern-matching is extremely easy:

db.get({ subject: "a" }, function(err, list) {
  expect(list).to.eql([triple]);
  done();
});

It even support a Stream interface:

var stream = db.getStream({ predicate: "b" });
stream.on("data", function(data) {
  expect(data).to.eql(triple);
});
stream.on("end", done);

Multiple Puts

LevelGraph also supports adding putting multiple triples:

var triple1 = { subject: "a1", predicate: "b", object: "c" };
var triple2 = { subject: "a2", predicate: "b", object: "d" };
db.put([triple1, triple2],  function(err) {
  // do something after the triples are inserted
});

Joins

LevelGraph also supports joins:

db.put([{
  subject: "matteo",
  predicate: "friend",
  object: "daniele"
}, {
  subject: "daniele",
  predicate: "friend",
  object: "matteo"
}, {
  subject: "daniele",
  predicate: "friend",
  object: "marco"
}, {
  subject: "lucio",
  predicate: "friend",
  object: "matteo"
}, {
  subject: "lucio",
  predicate: "friend",
  object: "marco"
}, {
  subject: "marco",
  predicate: "friend",
  object: "davide"
}], function () {

  var stream = db.joinStream([{
    subject: "matteo",
    predicate: "friend",
    object: db.v("x")
  }, {
    subject: db.v("x"),
    predicate: "friend",
    object: db.v("y")
  }, {
    subject: db.v("y"),
    predicate: "friend",
    object: "davide"
  }]);

  stream.on("data", function(data) {
    // this will print "{ x: 'daniele', y: 'marco' }"
    console.log(data);
  });
});

It also support a similar API without streams:

db.put([{
 ...
}], function () {

  db.join([{
    subject: "matteo",
    predicate: "friend",
    object: db.v("x")
  }, {
    subject: db.v("x"),
    predicate: "friend",
    object: db.v("y")
  }, {
    subject: db.v("y"),
    predicate: "friend",
    object: "davide"
  }], function(err, results) {
    // this will print "[{ x: 'daniele', y: 'marco' }]"
    console.log(results);
  });
});

It also allows to generate a stream of triples, instead of a context:

  db.join([{
    subject: db.v("a"),
    predicate: "friend",
    object: db.v("x")
  }, {
    subject: db.v("x"),
    predicate: "friend",
    object: db.v("y")
  }, {
    subject: db.v("y"),
    predicate: "friend",
    object: db.v("b")
  }], {
    materialized: {
      subject: db.v("a"),
      predicate: "friend-of-a-friend",
      object: db.v("b")
    }
  }, function(err, results) {
    // this will print all the 'friend of a friend triples..'
    // like so: { 
    //   subject: "lucio", 
    //   predicate: "friend-of-a-friend",
    //   object: "daniele"
    // }
  });

Deleting

Deleting is easy too:

var triple = { subject: "a", predicate: "b", object: "c" };
db.del(triple, function(err) {
  // do something after the triple is deleted
});

Navigator API

The Navigator API is a fluent API for LevelGraph, loosely inspired by Gremlin It allows to specify joins in a much more compact way and navigate between vertexes in our graph.

Here is an example, using the same dataset as before:

    db.nav("matteo").archIn("friend").archOut("friend").
      contexts(function(err, results) {
      // prints:
      // [ { x0: 'daniele', x1: 'marco' },
      //   { x0: 'daniele', x1: 'matteo' },
      //   { x0: 'lucio', x1: 'marco' },
      //   { x0: 'lucio', x1: 'matteo' } ]
      console.log(results);
    });

The above example match the same triples of:

    db.join([{
      subject: db.v("x0"),
      predicate: 'friend',
      object: 'matteo'
    }, {
      subject: db.v("x0"),
      predicate: 'friend',
      object: db.v("x1")
    }], function(err, results) {
      // prints:
      // [ { x0: 'daniele', x1: 'marco' },
      //   { x0: 'daniele', x1: 'matteo' },
      //   { x0: 'lucio', x1: 'marco' },
      //   { x0: 'lucio', x1: 'matteo' } ]
      console.log(results);
    });

It allows to see just the last reached vertex:

    db.nav("matteo").archIn("friend").archOut("friend").
      values(function(err, results) {
      // prints [ 'marco', 'matteo' ]
      console.log(results);
    });

Variable names can also be specified, like so:

db.nav("marco").archIn("friend").as("a").archOut("friend").archOut("friend").as("a").
      contexts(function(err, friends) {
 
  console.log(friends); // will print [{ a: "daniele" }]
});

Variables can also be bound to a specific value, like so:

db.nav("matteo").archIn("friend").bind("lucio").archOut("friend").bind("marco").
      values(function(err, friends) {
  console.log(friends); // this will print ['marco']
});

A materialized join can also be produced, like so:

db.nav("matteo").archOut("friend").bind("lucio").archOut("friend").bind("marco").
      triples({:
        materialized: {
        subject: db.v("a"),
        predicate: "friend-of-a-friend",
        object: db.v("b")
      }
    }, function(err, results) {
      
  // this will return all the 'friend of a friend triples..'
  // like so: { 
  //   subject: "lucio", 
  //   predicate: "friend-of-a-friend",
  //   object: "daniele"
  // }

  console.log(results); 
});

It is also possible to change the current vertex:

db.nav("marco").archIn("friend").as("a").go("matteo").archOut("friend").as("b").
      contexts(function(err, contexts) {

   //  contexs is: [{
   //    a: "daniele",
   //    b: "daniele"
   //   }, {
   //     a: "lucio", 
   //     b: "daniele"
   //   }]

});

TODO

There are plenty of things that this library is missing. If you feel you want a feature added, just do it and submit a pull-request.

Here are some ideas:

• Return the matching triples in the JOIN results.
• Support for Query Planning in JOIN.
• Add more database operators.

Contributing to LevelGraph

• Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
• Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
• Fork the project
• Start a feature/bugfix branch
• Commit and push until you are happy with your contribution
• Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
• Please try not to mess with the Makefile and package.json. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

Credits

LevelGraph builds on the excellent work on both the LevelUp community and the LevelDB and Snappy teams from Google and additional contributors. LevelDB and Snappy are both issued under the New BSD Licence.

LICENSE - "MIT License"

Copyright (c) 2013 Matteo Collina, http://matteocollina.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.